1. Field of the Invention
The present invention relates to an air-conditioning or a refrigerating system concentrically controlling a plurality of air-conditioners or refrigerators installed at separate positions and their related devices.
2. Description of Prior Art
There has so far been known an apparatus of this kind as shown in FIG. 1. In FIG. 1, a reference numeral 1 designates a central control unit, numerals 2a, 2b, 2c, 2d and 2e designate terminal control units for controlling air conditioners or refrigerators, a numeral 3 designates a backup control unit used for the central control unit 1 at the time of the breaking down of it, a numeral 4 designates a transmission line to transmit information for control from the backup control unit 3 to each of the terminal control units 2a, 2b, 2c, 2d and 2e and vice versa, numerals 5a, 5b, 5c, 5d and 5e designate loads such as air conditioners or refrigerators connected to each of the terminal control units.
The operation of the conventional control apparatus will be described.
Under ordinary circumstances, information to control each of loads 5a-5e, analogue data such as temperature and pressure for air conditioning or refrigerating operations and digital data such as operating condition or abnormal condition are input to each of the terminal control units 2a, 2b, 2c, 2d and 2e and the input data are transmitted to the central control unit 1 through the transmission line 4.
The central control unit 1 receives information to control each of the loads 5a-5e, information for registration such as a type of load, control mode, order of operations, information to be set such as temperature, time, and information for command such as start or stoppage by means of a key board, and performs operations for temperature control, timer control and so on by using the input information as above-mentioned and another input information supplied from each of the terminal control units 2a-2e.
A result of the operations is supplied to each of the terminal control units 2a-2e through the transmission line 4, as output data for controlling the loads 5a-5e.
Each of the terminal control units 2a-2e receives the output data; converts the output data into data capable of controlling each of the loads and gives an output for control, as a relay output, to each of the loads. However, if the central control unit 1 becomes faulty by any cause such as current service interruption, breakdown or run away, the result of operation for control, namely information for controlling the output of the loads disappears from each of the terminal control units 2a-2e whereby it is impossible to control the loads and the entire system is broken down. To avoid such disadvantage, there has been provided a backup control unit 3 which monitors the central control unit 1 and controls the terminal control units instead of the same at the time of breaking-down of the central control unit 1 to continue controlling operations for the entire system, and at the same time the backup control unit 3 generates an alarm of the breaking-down of the central control unit 1 to the outside of the system.
Since the conventional decentralization type control apparatus has been highly depending on the central control unit 1, if the central control unit is broken down by any cause, there has resulted breaking-down of the entire system. It has, therefore, been necessary to install a backup control unit having the same capacity as the central control unit to continue operations of the system. The provision of the back up control unit has necessarily pushed up a cost for the control apparatus.